Vacuum-tight electrical connections for electron-discharge devices



Nov, 26, 1957 R. K. GOODWIN 1 VACUUM-TIGHT ELECTRICAL CONNECTIONS FORELECTRON-DISCHARGE DEVICES Filed June 12, 1952 JNVENTOR. RONALD KENNETHGooowm Hi5 ATTQRN United States Patent 6 f VACUUM-TIGHT ELECTRICALCONNECTIONS F OR ELECTRON-DISCHARGE DEVICES Ronald Kenneth Goodwin,Hiliingdon, England, assignor to Cinema-Television Limited, London,England, a British company Application June 12, 1952, Serial No. 293,090

Claims priority, application Great Britain July 6, 1951 1 Claim. (Cl.49-78) This invention relates to improvements in vacuum-tight electricalconnections for electron discharge devices having vitreous envelopes andis more especially concerned with such devices in which it is requiredto make electrical connection between a conducting layer on the innersurface of an element of the envelope of the device and an externalcircuit.

The invention is especially applicable to devices in which one elementof the envelope comprises a disc or spherical shell of glass or othervitreous insulating material which is sealed to another vitreous portionof the envelope during the manufacture of the device and which carrieson its inner face a conducting layer to which electrical contact must bemade from outside the device. As a specific example, the invention isespecially useful for forming vacuum-tight connections to ametal-backing layer deposited over the fluorescent screen of acathoderay tube, image converter, or the like.

A known method of making such connections consists of rounding the edgeof a portion of the periphery of such an element, applying to therounded edge a layer of a material known in the art as platinumpaste-which comprises finely divided platinum mixed with a smallquantity of a finely divided binding material such as lead borosilicateand with a volatile carrier vehicle such as turpentineheating theelement in an oven to burn away or bake out the carrier vehicle from thepaste, and then locally heating the paste residue by means of a smallflame to cause the binder component of the paste to melt and to sinterthe platinum firmly to the glass. The element is thus provided with aconductor extending from the inner to the outer face and is then sealedto the remainder of the envelope of the device.

This known method suffers from the serious disadvantage that a largeproportion of seals made in this manner are found to leak, owing to thefact that chains of small bubbles tend to form or are trapped in thespace between the two portions of the envelope and the edges of thesintered metallic layer. These bubbles are not removed during the normalprocess of sealing, because the glass does not become sufficiently fluidduring this process to flow into this space. Tooling of the outercomponent of the envelope to force it into the space usually results inbreakage of the paste layer and a useless seal.

It is, therefore, an object of the present invention to provide animproved method of making vacuum-tight electrical connections inelectron-discharge devices constructed with vitreous envelopes, by theuse of which method the disadvantages of known techniques may be avoidedat little or no increase in cost.

According to the present invention there is provided a method of makinga vacuum-tight electrical connection to the interior of a vitreousenvelope which comprises the steps of applying to a component member ofthe envelope a layer of paste comprising a finely divided metal mixedwith a binding agent and a volatile carrier vehicle and extendingcontinuously from an inward to an out 2,814,165 Patented Nov. 26, 1957ward portion of the member, bevelling the lateral edges of the pastelayer over at least such portions as are to be enclosed within the sealbetween the member and a mating component member of the envelope,heating the paste layer to volatilize the carrier vehicle and to sinterthe metal and binder to the member, assembling the component member toits mating member, and sealing the members together.

This method results in a great reduction in the proportion of leakyseals produced, as the glass is able to flow smoothly on to theplatinum, making a vacuum-tight joint, without the necessity forexcessive tooling and consequent risk of breaking the conductor.

Where a metal is referred to in the specification and claims it is to beunderstood that a metal must be chosen which will not be attacked eitherby the atmosphere at the high temperatures to which it will be subjectedin the sealing process or by metallic vapours or gases which may be usedwithin the discharge device, and which will form a conductive layer whenthe finely divided metal is sintered to the glass in the presence of abinder such as lead borate.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may best beunderstood, however, by reference to the following description taken inconnection with the accompanying drawings in the several figures ofwhich like reference numerals indicate like elements and in which:

Figures 1-5 illustrate the preparation of an envelope element for aknown type of connection;

Figures 68 illustrate the construction of a joint using an elementprepared as described in relation to Figures 1-5; and

Figure 9 illustrates the form of a vacuum-tight connection preparedaccording to the present invention.

Figure 1 is a plan view of a circular glass window 11 which is to besealed into the envelope of an electron discharge device. To form aknown vacuum-tight connection the edge of this window, whosecross-section at the edge as exemplified by a section taken at 22 isshown in Figure 2, has a portion 1213 of its edge rounded off with aflame to give the form illustrated by the section at 3--3 shown inFigure 3. A layer of platinum paste is then applied With a brush to theedge of the window as shown at 14 in Figure 4. A section of the pastelayer taken at 55 will then appear as shown in Figure 5.

The window is then heated in an oven to a temperature of some 5006()0 C.to burn away the turpentine carrier vehicle and while still hot thepaste layer is locally heated with a flame to melt the paste binder andsinter the platinum firmly to the glass. The window is now sealed intothe envelope as shown in Figures 68.

Figure 6 shows a partial end view of the window 11 sealed to the body 15of the envelope, while Figure 7 shows a section through the seal at 7-7in Figure 6, and Figure 8 is a plan view of the same part of the joint.It will be seen that at the lateral edges 16 of the metal layer there isformed a sharp angle which is the cause of failures in the vacuum seal,for the glass of the envelope does not become fluid enough in thesealing process to penetrate fully into the angle, so that there is atendency for chains of air bubbles to form and become trapped as shownat 17.

According to the present invention, however, after the platinum pastelayer has been applied to the rounded edges of the window, the sharplateral edges 16 of the paste layer are smoothed down to a bevel, forexample by brushing in the direction from the top of the paste layer tothe adjacent window edge with a brush just moistened 3 with turpentineor such other carrier vehicle as is used. By this means, the paste layeris caused to assume the form illustrated in Figure 9, which shows acompleted seal made in accordance with the present invention. The window11 has a portion of its edge rounded, and the paste layer 14 appliedthereto has its lateral edges bevelled off as shown at 18. The window isthen assembled in the body 15 of the envelope and sealed to it in knownmanner.

While the invention is described as utilizing platinum paste, it isapparent that other preparations of similar nature may be used withequal success, provided that the essential feature of producing bevelledlateral edges for the metal layer before sealing is employed.

In any case, 'a seal of this nature is normally limited in its use tocarrying currents of the order of a few microamperes, as the metalliclayer produced is very thin and might be broken by the passage of highercurrents. If larger currents are to be passed, either a number ofconnections must be connected in parallel or the peripheral extent ofthe paste layer must be increased, possibly until it completelyencircles the window and thus eliminates the edges at which air bubblesmay be trapped.

While a particular embodiment of the present invention has been shownand described, it is apparent that various changes and modifications maybe made, and it is therefore contemplated in the appended claim to coverall such changes and modifications as fall within the true spirit andscope of the invention.

I claim:

The method of making a vacuum-tight electrical connection to theinterior of a vitreous envelope which comprises the steps of: applyingto a first vitreous component member of said envelope a layer of pastecomprising a finely divided metal mixed with a binding agent and avolatile carrier vehicle, said layer extending continuously from aninward portion, over a peripheral portion and to an outward portion ofsaid member; bevelling the lateral edges of that part of said pastelayer which extends over said peripheral portion of said member andwhich will be enclosed within the seal between said first member and avitreous mating component member of said envelope; heating said layer tovolatilize the vehicle and to sinter the metal and binder to said firstmember; assembling said first component member to its mating member withsaid part of said sintered layer sandwiched therebetween; and sealingsaid members together.

References Cited in the file of this patent UNITED STATES PATENTS1,293,441 Houskeeper Feb. 4, 1919 2,170,602 Bauer Aug. 22, 19392,198,578 Hazleton Apr. 23, 1940 2,235,680 Haven et al Mar. 18, 19412,265,352 Corbin Dec. 9, 1941 2,282,106 Underwood May 5, 1942 2,454,270Braunsdorft Nov. 23, 1948 2,461,878 Christensen Feb. 15, 1949 FOREIGNPATENTS 22,911 Great Britain of 1906

